Thermal printers have found widespread use in a number of applications because of their advantages, which include non-impact operation and very low noise level. The utility of thermal printers generally has been somewhat limited, however, due to relatively low operating speed. In large part, this is caused by thermal inertia; that is, when the individual thermal elements of a thermal printer, such as one of the dot matrix type, for example, are heated to the temperature necessary to produce the desired recording on the record medium on which printing is to be effected, a time interval for cooling is necessary before the thermal printer matrix can be used for the next operation; otherwise spurious recording will result from elements which have not cooled below a critical temperature. Particularly during high speed printing, peak temperatures of the print elements become higher and higher as time passes when sufficient cooling time is not allowed between burns. After a short time in such a situation, the temperature values reached at the end of the cool period could be above the threshold temperature of the thermal paper or thermal transfer ribbon being used with the printer.
A partial solution has been found in the past to this temperature build-up problem by reducing the time duration of the current pulses which are applied to the thermal elements or by reducing the magnitude of the applied current. However there comes a point, as the burn time duration approaches zero or as the initial temperature of the element approaches the threshold temperatures, that further control is no longer feasible. In a line printer application, for example, the thermal print head can be driven at the highest speeds only when all elements are driven simultaneously. The large energy build-up as such a printer cycles will cause a rapid decrease in operating speed, due to the necessity to pause between cycles until the element temperatures cool below the threshold values. It should also be noted that other heat generating sources are usually present in a thermal printer environment, such as stepper motors, for example. These speed constraints become more extreme as the size of the printer is increased, of course.